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• mdct15 : simplify prereindexing and forward transform postrotation

  25 juillet 2017, par Rostislav Pehlivanov

  mdct15 : simplify prereindexing and forward transform postrotation
  Equivalent.
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

  • [DH] libavcodec/mdct15.c

• Reading RTSP stream with FFMpeg library - how to use avcodec_open2 ?

  29 avril 2015, par Abstraction

  While trying to read rtsp stream I get some problems, with code and documentation alike. Short description : whatever I do, avcodec_open2 either fails (saying "codec type or id mismatches") or width and height of codec context after the call are 0 (thus making further code useless). Stream itself can be opened normally by VLC player and av_dump_format() displays correct info. My code is based on technique answer to this question.

  Long description : my code is in C#, but here is C++-equivalent of FFMpeg calls (I actually reduced my code to this minimum and problem persists) :

  av_register_all();
  
  avformat_network_init(); //return code ignored
  
  
  
  AVFormatContext* formatContext = avformat_alloc_context();
  
  if (avformat_open_input(&formatContext, stream_path, null, null) != 0) {
  
      return;
  
  }
  
  
  
  if (avformat_find_stream_info(formatContext, null) < 0) {
  
      return;
  
  }
  
  
  
  int videoStreamIndex = 0;
  
  for (int i = 0; i < formatContext->nb_streams; ++i) {
  
      AVStream* s = formatContext->streams[i];
  
      if (s->codec == null) continue;
  
      AVCodecContext c = *(s->codec);
  
      if (c.codec_type == AVMEDIA_TYPE_VIDEO) videoStreamIndex = i;
  
  }
  
  
  
  //start reading packets from stream and write them to file
  
  //av_read_play(formatContext); //return code ignored
  
  //this call would print "method PLAY failed: 455 Method Not Valid in This State"
  
  //seems to be the case that for rtsp stream it isn't needed
  
  
  
  AVCodec* codec = null;
  
  codec = avcodec_find_decoder(AV_CODEC_ID_H264);
  
  if (codec == null) {
  
      return;
  
  }
  
  
  
  AVCodecContext* codecContext = avcodec_alloc_context3(null);
  
  avcodec_get_context_defaults3(codecContext, codec);//return code ignored
  
  avcodec_copy_context(codecContext, formatContext->streams[videoStreamIndex]->codec); //return code ignored
  
  
  
  av_dump_format(formatContext, videoStreamIndex, stream_path, 0);
  
  
  
  if (avcodec_open2(codecContext, codec, null) < 0) {
  
      return;
  
  }

  The code actually uses DLL version of FFMpeg library ; avcodec-55.dll and avformat-55.dll are used.

  Documentation says something weird about which calls can be made in which succession (that copy_context should be called before get_context_defaults), current code is left close as possible to technique version. As written, it results in non-zero return from avcodec_open2 with "codec type or id mismatches" message. Changing the order does little good : now avcodec_open2 executes successfully, but both codecContext->width and codecContext->height are 0 afterwards.

  Also documentation doesn’t mention which is default value for the third argument of avcodec_open2 should be, but source code seems to taking into account that options can be NULL.

  Output of av_dump_format is as follows :

  Input #0, rtsp, from 'rtsp://xx.xx.xx.xx:xx/video.pro1':
  
    Metadata:
  
      title           : QStream
  
      comment         : QStreaming Media
  
    Duration: N/A, start: 0.000000, bitrate: 64 kb/s
  
      Stream #0:0: Video: h264 (Baseline), yuvj420p(pc), 1920x1080, 30 fps, 25 tbr, 90k tbn, 60 tbc
  
      Stream #0:1: Audio: pcm_mulaw, 8000 Hz, 1 channels, s16, 64 kb/s

• How to convert/mux/encapsulate AAC-ADTS into M4A on Xamarin Android 4.1+ ?

  27 août 2014, par Ingolmo

  I’m making an Android 4.1+ app with Xamarin, which is mixing two audio files in a resulting AAC-ADTS file, using the MediaCodec API.
  The problem is that this file is not readable by most audio players, or on the iOS version of the app...

  I’m now trying to encapsulate the AAC-ADTS data inside a MP4/M4A container. I found many possible solutions, but I’m not able to implement properly one of them.

  • Android provides the "MediaMuxer" API, which seems capable of doing that... But this is only available on Android 4.3, which is not acceptable for me.

  • https://github.com/sannies/mp4parser this Java library seems to do the work, but I cannot manage to build the Java binding for it (details here), and I did not find any equivalent C# library.

  • I tried to build ffmpeg for Android, but did not manage to make it work (ffmpeg does not find the file on the phone). I don’t really understand the underlying problems, but I mainly don’t know how to build and use ffmpeg so it is compatible on every Android phone, since the architectures may differ.

  Is one of these solutions the "good one", and if so, can you provide me links or help to do it properly, or am I missing a more consistent solution ?